Miniature device for generating a multi-polar field, in particular for filtering or deviating or focusing charged particles

ABSTRACT

The invention relates to a micro-device for generating a multi-polar transverse field, or a micro-device for the filtration or the deflection or the focusing of charged particles, comprising n longitudinal conductive micro-beams ( 32, 34, 36, 38 ), of polygonal cross section, and arranged around a longitudinal axis (AA′).

TECHNOLOGICAL FIELD AND PRIOR ART

The invention relates to the field of electrode architectures thatpermit the generation of a multi-polar field, or permit the filtrationor the deflection or the focusing of charged particles. Moreparticularly, the invention relates to micro-devices that integrateassemblies of micro-electrodes, also for the purpose of generating amulti-polar field in particular for the filtration or deflection orfocusing of charged particles.

The invention finds application notably in the field of massspectrometry: in effect, the assemblies of electrodes according to theinvention can be used in mass spectrometers. The invention thereforealso relates to the field of mass spectrometry.

Mass spectrometry is an analysis technique widely used in laboratoriesand in industry. Using mass spectrometry the nature of constituents of agas can be determined with a sensitivity better than ppm. To do this,the gas to be analyzed must be at low pressure, in general less than10⁻⁴ mbar. This is a limitation for applications where the pressure isgreater (10⁻² mbar) and for which it is then necessary to add pumps andsupplementary circuits so as to reduce the pressure in the area wherethe mass spectrometer is. The creation of a spectrometer of small size(≈1 cm³) would allow one to work under a lower level of vacuum.

In a general way, a mass spectrometer comprises three distinct parts, asillustrated in FIG. 1: an ionization chamber 2, a separator 4 (filter)and an ion detector 6. Many separators are of the quadrupolar type. Thetheory of uni-polar and quadrupolar mass spectrometers etc is forexample described in the book “Techniques de l'Ingénieur”, volume P3, P2615, p. 1-39. The mass filter 4 is the place where, through the set ofelectromagnetic forces, the ions of different masses are separated. In aquadrupole (an accepted term meaning “a mass analyzer fitted with aquadrupolar type filter”), a high frequency electric field is generatedbetween 4 parallel bars 8, 10, 12, 14 such as those shown in FIG. 1. Itis assumed that the ions move along the mean direction OZ parallel tothe bars.

In a general way, a quadrupolar electric field is such that itsamplitude is a linear function of the co-ordinates. The electricalpotential is therefore a quadratic form of the co-ordinates. It can bewritten in the form V=(φ/r²)×(x²−y²) where r is the distance between theaxis OZ and the bars (r is also called the throat radius of thequadrupole) and φ a constant value of the potential. In order to obtainsuch a potential distribution, two opposite bars are polarized to +V,while the two others are polarized to −V.

In the case of a quadrupole being used as a filter or a means offocusing or of deflection, the potential V in addition comprises a timedependent component (term in cos ωt) which is used to make the chargedparticles oscillate. The lines of equipotential, which, at a givenmoment, correspond to this distribution of potentials (as a function ofthe potentials applied to the bars) are hyperbolae in the plane XOY. Inthe ideal case, the cross sections of the bars have this same hyperbolicform. A quadrupolar system with bars 16, 18, 20, 22 of hyperbolicsection is illustrated in FIG. 2 and is, for example, described in U.S.Pat. No. 5,373,157.

In the majority of cases, and in order only to use machining that iseasy to carry out, the bars have circular cross sections osculating tohyperbolae at their peak; such cross sections 26, 28, 30, 32 are alsoshown in FIG. 2. A degradation of resolution results from passing fromthe hyperbola to the circle.

If one wishes to reduce the size of a quadrupolar spectrometer to about1 cm³, all the dimensions of the filter are affected by this, inparticular the radius of the bars, their distance to the center and, ofcourse, their length.

Document WO-96/31901 describes a miniaturized quadrupolar massspectrometer. This device uses cylindrical beams made from metal coatedoptical fibers. In such a device, the insulators situated between thecylindrical bars can lead to charge effects which are prejudicial to theoperation of the device.

The patent U.S. Pat. No. 5,401,962 describes a miniature quadrupole. Inthis document, the miniaturization or the reduction in size, originatesfrom the assembly of a plurality of quadrupoles in parallel. This devicelacks resolution. Furthermore, its production, even when it usescylindrical electrodes is rather time consuming.

Document U.S. Pat. No. 4,994,336 describes a control plate for alithography device. This control plate essentially comprises asemi-conductor substrate in which a window or opening is made to allowthe passage of beams of particles. Deflection elements allow the beamsto be deflected.

This document also describes methods of producing such a plate. In thesemethods, the deflection elements are obtained by etching a layer toproduce depressions in it that have the shape of deflection elements.The deflection elements are then created along a direction perpendicularto the plane of these layers.

Finally, in this document, the field generated is a uniform field in alldirections and in all the space between the flat electrodes. This fieldis not multi-polar.

DESCRIPTION OF THE INVENTION

The problem posed therefore is that of producing components, notably fortheir application to mass spectrometry, that allow among other thingsthe miniaturization of the spectrometers.

In particular, the problem is posed of creating assemblies of electrodeswhich would enable easy production of micro mass spectrometers.

More precisely, a subject of the invention is a micro-device forgenerating a multi-polar transverse field, comprising n conductivelongitudinal micro-beams of polygonal cross section, arranged around alongitudinal axis.

Advantageously, the field is constant along the longitudinal axis.

By a multi-polar field one understands any electrical field, even amono-polar one. Such a field is not uniform since it is multi-polar ormono-polar.

Consequently, according to the invention, the creation of electricfields on a sub-millimeter scale, and which are derived from potentialswhich are for example, of the quadrupolar, hexapolar or octopolar typeor more generally are N-polar (N>1) can be carried out with electrodestructures (also called lenses) in which the electrodes have a crosssection of polygonal shape. Such electrodes are compatible withproduction using micro-electronic or micro-technology techniques andtherefore permit the manufacture of miniaturized mass spectrometers.

Another subject of the invention is a micro-device for the filtration orthe deflection or the focusing of charged particles, comprising nconductive longitudinal micro-beams, with polygonal cross section, andarranged around a longitudinal axis of propagation of the chargedparticles.

Another subject of the invention is a micro-device for the filtration,or the deflection or the focusing of charged particles that comprises amicro-device to generate a multi-polar transverse field such as thatalready described above.

For this, the invention specifies an electrode structure for amicro-device for filtration, or deflection or focusing, which iscompatible with production by the techniques of micro-electronics ormicro-technology. Electric fields can also be generated for amicro-device for filtration, or deflection or focusing on asub-millimeter scale.

At present, the electrodes used in a quadrupolar type device, or moregenerally an N-polar device, have sizes which cannot be reduced belowcertain dimensions, which limits the lower size of the device. Inparticular, document U.S. Pat. No. 5,401,962 mentions cylindricalelectrodes of a diameter between 0.5 mm and 1 mm, and of a lengthbetween about 1 cm and 2 cm. The electrode structure according to theinvention allows sub-millimeter devices to be produced (for example withbars whose thickness is a few hundreds of μm) which are able to work athigher pressure (for example about 10⁻² mbar).

The assembly in parallel of several multi-polar structures according tothe invention allows the intensity of the output signal from this samestructure to be increased. The production of such a structure proceedsthrough the production of certain parts of the structure in anindividual way, and then through a step of assembling these parts, inparallel.

Means of polarizing the conductive micro-beams can be connected to themulti-polar structures according to the invention. Similarly, means canbe linked to them of introducing ions or charged particles along adirection defined by the longitudinal axis or axes. A multi-polar fieldis linked to each longitudinal axis, all the longitudinal axes beingparallel.

According to one particular embodiment, each micro-beam can be producedin a flat substrate and held in the plane of the substrate by supportbars.

The micro-device can comprise:

at least first and second sheets made of insulating or semiconductormaterial

means that allow the sheets to be held parallel at a certain distancefrom one another,

areas etched into each sheet to define micro-beams in them.

The micro-device comprises for example

first, second and third sheets made of insulating or semiconductormaterial,

means that allow the first and second sheets to be held parallel at acertain distance from one another,

means that allow the second and third sheets to be held parallel at acertain distance from one another,

areas etched into each sheet defining micro-beams in them.

The means of holding the sheets parallel to one another may, inaddition, permit alignment of said sheets in a way that provides thedesired multi-polar field. For example, these means are cross membersarranged in slots created in the sheets to ensure this alignment.

These structures are totally compatible with collective and extremelyprecise production (to about ±1 μm), which can be implemented usingetching techniques and working techniques known in the field ofmicro-electronics.

Another subject of the invention is a mass spectrometer comprising amicro-device according to the invention, such as that described above,means of introducing ions and means of detection.

Finally, a subject of the invention is a method of producing amicro-device for generating a multi-polar transverse field and inparticular a micro-device for the filtration, or the deflection or thefocusing of charged particles, comprising the following steps:

etching P substrates made of insulating or semiconductor material insuch a manner as to define, in each substrate one or more micro-beams,

coating the micro-beams with metal

assembling P etched substrates in parallel with one another.

BRIEF DESCRIPTION OF THE FIGURES

The characteristics and advantages of the invention will better becomeapparent in the light of the description which follows. This descriptionfocuses on embodiment examples given for purposes of explanation whichare not limitative and which make reference to the appended drawings inwhich:

FIG. 1 diagrammatically represents a quadrupolar type mass analyzer,

FIG. 2 illustrates the creation of quadrupoles using hyperbolic orcylindrical electrodes,

FIG. 3 represents the embodiment of a quadrupole according to theinvention,

FIGS. 4A and 4B represent, in section and in a view from above, adetailed embodiment of a quadrupolar system according to the invention,

FIG. 5 diagrammatically represents a ladder of micro-beams,

FIG. 6 is a plan view of a quadrupole assembly operating in parallel,

FIGS. 7A and 7B represent in section and in a view from above, amultiple quadrupole according to the invention machined bymicro-technology,

FIGS. 8A to 8C represent results of filtration simulation around massM=10, using a spectrometer with cylindrical bars,

FIGS. 9A and 9B represent potentials obtained with cylindrical bars(FIG. 9A) or square section bars (FIG. 9B),

FIGS. 10A to 10C represent results of filtration simulation around massM=10 using a spectrometer with bars of square section.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A structure for the creation of a quadrupole according to the inventionis illustrated in FIG. 3. In accordance with this structure, electrodes32, 34, 36, 38, of polygonal cross section, are arranged parallel to oneanother and in a symmetrical manner with respect to an axis AA′. Thepolygonal section shown in FIG. 3 is a square section, but otherpolygonal sections (pentagonal, hexagonal, etc.) can be created withinthe scope of the invention. In the case of a square cross section, theside of the square e may, for example be equal to 0.5 mm (or less) andthe electrode, for example, has a length of the order of 10 mm.

Below, examples are given for which the bars have thicknesses of about300 μm or 500 μm.

This electrode assembly constitutes a quadrupolar structure that can beused for example in the context of a mass spectrometer. Such aquadrupolar structure is then coupled on the one hand to a source ofions (situated at one end of the quadrupolar structure) and on the otherhand to an ion detection system (situated at the other end of thequadrupolar structure). Examples of such sources of ions and suchdetection systems are described in the book “Techniques de l'Ingénieur”,volume P3, P 2615, p. 1-39.

Each of the electrodes is connected to means of applying a certainpotential to it. The result is an electric field in the space betweenthe four electrodes, and around the axis AA′. If the generated electricfield is a quadrupolar electric field, its amplitude will be a linearfunction of the X, Y and Z co-ordinates.

When the quadrupole is used as a filter or a means of deflection or offocusing the beam of particles 40, the potential V additionally includesa time dependent component (a cos ωt term) which allows the chargedparticles to be oscillated.

An embodiment of a quadrupolar system according to the invention isillustrated in a more precise way in FIG. 4A. In this Figure, referencenumbers identical to those in FIG. 3 designate the micro-beams, ofpolygonal section (in this case square), of the quadrupolar device. Thedevice also comprises cross members 40, 42, that permit separation ofthe upper plane 44, in which the upper micro-beam 32 is produced, fromthe intermediate plane 46, in which the two micro-beams 34, 38 areproduced, and, on the other hand, the intermediate plane 46 from thelower plane 48 in which the micro-beam 36 is produced. FIG. 4Brepresents a view from above of this device: the upper micro-beam 32 isobtained, for example, by etching and partial or total metal coating ofa wafer of insulating or semiconductor material that defines the plane44. The length l of the windows created by etching in the plane 44 isabout 20 e (where e is the thickness of a micro-beam).

Similarly, the micro-beams 34, 38 are obtained by etching and partial ortotal metal coating of a wafer of insulating or semiconductor materialthat defines the plane 46 and the lower micro-beam is obtained byetching and partial or total metal coating of a wafer of insulating orsemiconductor material that defines the lower plane 48. The thickness eof the bars is then determined by the thickness of the wafers ofinsulating or semiconductor material which have been etched. Forexample, one can have bars or micro-electrodes of thickness 300 μm or500 μm. For a thickness of 500 μm, the upper bar or micro-electrode 32is positioned at a distance d approximately equal to 0.74e=0.74×500=370μm from the bars 34, 38.

In FIG. 4B, reference numbers 50, 52, 54, 56 designate support barswhich link the micro-beam 32 to the rest of the plane 44. In each of theother planes, 46, 48, such support bars support the micro-beams and linkthem to one another or to the etched substrate.

Slots 60, 62, 64 are also created in the various wafers of material soas to be able to position the cross members 40, 42.

If these slots are created by etching the wafers of material, they wouldhave a thickness equal to the distance separating two parallel planesincreased by the depth of etching in each of the sheets of material.Returning to the example above, and assuming that the slots 60, 62, 64are etched over a depth of 10 μm, the cross members 40, 42 would have atotal height of: 370+10+10=390 μm.

The cross members can be produced, depending on the length of thedevice, in a single block or in several blocks. For example, in FIG. 4B,reference numbers 40-1, 40-2, 40-3 and 42-1, 42-2, 42-3 designate thelocations of six cross members (three aligned cross members for eachside) which separate the upper 44 and intermediate 46 planes. In a viewfrom above, each cross member has small dimensions c₁, c₂, each forexample equal to or less than 1 mm. There can be several cross memberson each side; however, preferably, each cross member is of a small size,so that the ions which are away from the central longitudinal axis ofthe apparatus, along which they are being propagated, will not bedeposited on them, which would lead to undesirable charge effects.

A method of producing such a structure will now be described. Firstly,one selects wafers in which the upper 44, intermediate 46 and lower 48planes of the structure will be created. Such wafers can be siliconwafers, of thickness e ranging for example from 0.5 mm. One thenproceeds to the following steps 1 to 4.

1)—The upper 44 and lower 48 sheets are etched (deep etching) in orderto make apparent on the one hand, the central bars 32, 36 and on theother hand, the slots 60, 62 which will be used for positioning and thefixing of the assembly. Known techniques employing masks and lithographyare used before etching. The deep etching operation occurs in two stagesso as to be able to keep four support bars 50, 52, 54, 56, preferably asfine and small as possible, their role being to support the central bar32, 36. First of all, each sheet is etched on one side to the extentthat the thickness of the support bar is preserved and then on the otherside in order to unblock it at the same time preserving the support bar(thanks to a second lithography step).

2)—The intermediate sheet (possibly in two pieces), of the samethickness as the preceding sheets, is etched so as to define the right34 and left 38 bars and the slots 64 for the cross members.

3)—Partial or total metal coating of the bars allow one to apply variousvoltages from connection electrodes to the four bars.

4)—Cross members 40, 42 made of insulating material (SiO₂) are etched sothat, on the one hand, they can be housed in the slots 60, 62, 64created on the three preceding sheets and, on the other hand, they havethe thickness required to separate the three sheets (in this case, thespace between the sheets is, for example, 0.74e). For application tomass spectrometry, the following steps can be added

5)—A mini ionization chamber and a detector of the Faraday cage type oran electron multiplier are added to the filter assembled in this way.Inlet and outlet orifices for the ions will be aligned along the axis ofeach quadrupole. Possibly, electrodes which are used as an electrostaticshield or a focusing lens to bring the ion beam to the inlet to thefilter are added to the system. With respect to the ionization, thisoccurs by known methods (ionization by electron beams coming from afilament or micro-tip or micro-edge cathode, or arising from adischarge). Detection takes place using traditional devices.

The method described above makes use of techniques that come from thefields of micro-technology and micro-electronics and permits thecreation of square or polygonal section bars with great precision. Suchtechniques are compatible with collective manufacture that allows one tospecify precise dimensions for the whole of the architecture (anaccuracy of the order of a micrometer can be achieved) the more so whena part of the assembly can be carried out at the time the bars aremanufactured. The techniques of deep etching of silicon wafers knownwithin the field of micro-technology or micro-electronics allow one toobtain rectangular sections starting with wafers with parallel surfaces.Similarly, the anisotropy of etchings dependent on crystalline surfacesallows one to obtain polygonal profiles.

Besides coupling them to a source of ions and/or an ion detection systemand going beyond the assembly in FIG. 4A, the electrodes can be mountedat their ends, onto two support plates parallel to one another, eachplate having slits or inlets or outlets required for the path of theions. This device can be produced, in micro-technology, by a methodknown by the name of “LIGA”

The structure described above is a quadrupolar structure, for examplefor providing a quadrupolar electric field. This structure can begeneralized to the production of an assembly of n conductivemicro-beams, of polygonal cross section, that allow one to obtain amulti-polar transverse field (and, advantageously a longitudinallyuniform field).

The invention also relates to the creation of a multiple structure, forexample of an assembly of quadrupoles operating in parallel. Thereduction, by a factor k, of the dimensions of a quadrupole, leads tothe reduction, by a factor k², of the inlet slit. So as to preserveenough signal without increasing the size of the slits (which would leadto deterioration in the resolution at high mass), one compensates forthis attenuation by placing a k² quadrupole in parallel. The gain involume is therefore a factor k, and the sensitivity remains the same.

For example, if all the dimensions are reduced by 2, the quadrupole isreduced, in weight and in volume, by a factor 2³=8. The inlet slit isreduced by a factor 2²=4. By placing four quadrupoles in parallel, eachwith new reduced slits, the same surface area of slit inlet is obtainedand a total volume is equal to 4×(⅛)=0.5 times the volume of theoriginal quadrupole before reduction. Hence one gains by a factor of 2as a minimum and even more, since one or more bars are common forseveral quadrupoles in parallel. So as to maintain or to increase theintensity of the total signal received by the detector, one cantherefore create a structure of quadrupoles (or n-poles) mounted inparallel.

Hence, one can create “ladders” of bars, of square or polygonal crosssection, that one can then assembly parallel to one another usingmicro-technology techniques. Such a ladder is illustrated in FIG. 5,where reference numbers 70, 72, 74, 76 designate individual poles,connected in a fixed manner to one another by support structures 78, 80at each of their ends.

FIG. 6 is a view, from the side of the ion inlet face, of an assembly ofquadrupoles operating in parallel. Each of the ladders corresponds to aline of black or white squares. Each individual quadrupole (for examplethat defined in FIG. 6 by the bars 82, 84, 86, 88) has a micro-beam incommon with the quadrupole next to it on the same line (in FIG. 6 thisis the quadrupole defined by the micro-beams 90, 92, 94, 84).

So as not to obstruct the ion inlet, one can choose to make ladders inwhich one out of two micro-beams is positively polarized (for examplethe black bars in FIG. 6), the others being negatively polarized. Onecan also choose to make the ladders with all the bars having the samepolarization (all blacks or all whites): in this case, a slit will bemade on each side, in order to define an inlet slit and an outlet slitfor the ions.

The creation of a multi-lens (or a multiple structure of the typedescribed above in connection with FIG. 6) calls upon the same type ofmicro-technology as that explained above for the creation of a singlelens or a single quadrupole.

FIG. 7A illustrates the production of two quadrupoles arranged side byside, the micro-beams being designated by reference numbers 82-94.

As in the case of the structure illustrated in FIG. 4A, the micro-beamsare produced in flat etched substrates 96, 98, 100, the assembly ofwhich is carried out with the help of cross members 102, 104 forseparation.

FIG. 7B represents a view from above of the structure of FIG. 7A. Eachmicro-beam 82, 90 is supported by support bars 106, 108, 110, 112, 114,116 created by etching the wafer 96.

Similarly, in the plane of the intermediate wafer 98, the micro-beam 84is supported by similar bars. Preferably, these bars are made as fineand as small as possible, so that they are not an obstacle to the ionsincident to or emerging from the quadrupoles, or the multipoles.

For example, the bars have lengths of 1240 μm (0.74e+e+0.74e) for asection of 10 μm×10 μm (the dimensions are given to ±1 μm).

The inlet and outlet orifices for the ions are aligned on the axis ofeach quadrupole: the points A and B in FIG. 7B are the paths of theseaxes in this Figure.

A comparative simulation of a traditional quadrupole (with an electrodeof circular section) and a quadrupole with a square bar (conforming tothe invention) has been carried out.

The study of the movement of an ion (confined to the central region,close to the axis of the quadrupole), under a potential dependent onvariables x, y, z and time, for a given quadrupolar configuration ispossible in an analytical manner or by simulation. The potentials +V and−V are variable in time so that the ion is successively attracted by onegroup of electrodes and then attracted by the two other electrodes, thisbeing in a cyclical manner.

A)—Case of the traditional quadrupole: bars of circular section ofradius r₀=0.39 mm, with a throat radius of 0.45 mm were considered. Thelength of the bars is of the order of 10 mm; such a value can beconsidered to be large in relation to the transverse dimensions andallows a certain number of oscillations of the ion along its path. Thepolarization of the electrodes as a function of time is simulated usingan electronic optical program (SIMION program, version 4.0, D. A. Dahland J. E. Delmore, Idaho National Engineering Laboratory, 1988). Thesolution chosen to fix the voltages U and V (DC part and AC part of thepotential applied to the bars) is that used by the majority ofmanufacturers (U/V ratio=0.17).

The FIGS. 8A-8C are an example of the results obtained, for a filtrationaround mass M=10 (M=9: FIG. 8A, M=10: FIG. 8B and M=11: FIG. 8C). Inthese Figures, only half of each bar is represented. From these Figures,it may be observed that for a kinetic energy of 10 eV in the directionof the quadrupole axis, the atomic mass 9 oscillates a certain number oftimes and then diverges after 3 mm of trajectory, the atomic mass 10remains stable under oscillation (and hence passes through the filter)while atomic mass 11 diverges after 4 mm of unstable oscillatingtrajectory.

B)—Case of the quadrupole with square bars: in this case, we firstsought to check that potential conditions in the central region(hyperbolic shapes), similar to those obtained with the bars of circularsection, could be provided with bars of square or polygonal section.This is what was done and it was possible to show, by simulation, thatthe use of square bars of small section allows one to obtain the samemap of electrical potential in the central region of the quadrupole asthat obtained using bars of round section. FIGS. 9A and 9B shows thejuxtaposition of the equipotentials of a model with bars of roundsection (cylinders of diameter 2×r (=0.78 mm), FIG. 9A) and another withsquare section bars (square beams with a side a=0.46 mm, FIG. 9B). Thesurfaces of the square beams being further from the axis of thequadrupole than those of the cylinders, a higher potential is applied tothese electrodes. In the case studied, the potential is doubled toobtain the same map of potential at the center.

FIGS. 10A to 10C represent the filtration of mass 10 (in comparison withmasses M=9 and M=11) in the case of a spectrometer with bars of squaresection. It may be observed that the filtration takes place just as wellas with the cylindrical bars.

The micro-beam structure according to the invention allows the creationof electrodes with controlled geometry. This geometry allows one toprovide results both as far as the electric field and the filteringcapacity are concerned that are as good as those from cylindricalelectrodes. Furthermore, the geometry proposed is compatible withproduction using techniques from micro-electronics, which allowcollective manufacture: techniques of etching substrates orsemiconductor wafers are in effect well controlled. Consequently, theelectrode structure according to the invention allows a device to beproduced that has good resolution as well as good performancereproducibility and the cost of which is low in comparison with devicesthat are currently known.

The devices according to the invention can be used in all fields of massspectrometry, where knowledge of the nature of gases and pollutants isdesired (for example in the environmental field or in themicro-electronics industry). Even at reduced resolution, for example atΔM=±3, such an instrument (or sensor) can be of interest. In effect, forexample, contamination by hydrocarbons is detectable between masses 50and 60, without other masses which disrupt the analysis being in thisrange: a reduced resolution can then be tolerated.

What is claimed is:
 1. A micro-device for the filtration or the focusingof charged particles comprising n conductive longitudinalmicroelectrodes, arranged around a longitudinal axis of propagation ofthe charged particles, characterized in that the n microelectrodes aremade up of P monolithic blocks, each comprising one or moremicroelectrodes of polygonal cross section, P being a whole numbergreater than or equal to 2, the P blocks being assembled in parallelwith one another in such a way that the microelectrodes are adapted togenerate a non-uniform electric field in a plane perpendicular to thelongitudinal axis.
 2. A micro-device according to claim 1, characterizedin that each block is created in a flat substrate and in that itcomprises support bars to rigidly link the microelectrodes of the block.3. A micro-device according to claim 2, characterized in that the flatsubstrate is a sheet of insulating or semiconductor materials in whichetched areas define the microelectrodes and in that it comprises meansfor holding the sheets parallel at a certain distance from one another.4. A micro-device according to claim 3, the means that permit the sheetsto be held parallel in addition carrying out an alignment of thesesheets in a way that provides a multi-polar field.
 5. A micro-deviceaccording to claim 4 characterized in that the etched areas of the sheetalso define the support bars.
 6. A micro-device according to claim 3characterized in that the etched areas of the sheet also define thesupport bars.
 7. A micro-device according to claim 3, the means forholding the sheets at a distance from one another comprising insulatingcross members.
 8. A micro-device for the filtration or the focusing ofcharged particles comprising a plurality of micro-devices according toclaim 2, assembled in parallel, along a plurality of longitudinal axes.9. A micro-device for the filtration or the focusing of chargedparticles comprising a plurality of micro-devices according to claim 1,assembled in parallel, along a plurality of longitudinal axes.
 10. Amicro-device according to claim 1, comprising in addition means ofpolarizing said conductive microelectrodes.
 11. A micro-device accordingto claim 1, comprising, in addition, means of introducing chargedparticles or causing them to enter along a direction defined by saidlongitudinal axis, or along directions defined by the longitudinal axes.12. A mass spectrometer comprising a micro-device according to claim 1,and means of introducing ions into the micro-device and detection means.13. A method of producing a micro-device for generating a multi-polartransverse field or a micro-device for the filtration, or the focusingof charged particles, comprising the following steps: etching Psubstrates made of insulating or semiconductor material in such a manneras to define, in each substrate one or more longitudinal microelectrodesof polygonal cross section, P being a whole number greater than or equalto 2, assembling P etched substrates in parallel with one another, insuch a way that the microelectrodes are arranged around one or morelongitudinal axes of propagation of the charged particles, and areadapted to generate a non-uniform electric field in a planeperpendicular to the longitudinal axis.
 14. A method of producing amicro-device for generating a plurality of multi-polar transverse fieldsor a micro-device for the filtration or the focusing of chargedparticles, comprising: the creation of individual micro-devices eachpermitting the generation of a multi-polar transverse field, or eachpermitting the carrying out of the filtration or the focusing of chargedparticles, and each comprising n conductive longitudinal microelectrodesof polygonal cross section, and arranged around a longitudinal axis,these microelectrodes are adapted to generate a non-uniform electricfield in a plane perpendicular to the longitudinal axis, the assembly,in parallel, of the micro-devices obtained during the preceding step.15. A mass spectrometer comprising a micro-device according to claim 7,and means of introducing ions into the micro-device and detection means.